Most national polls show Democratic presidential candidate Hillary Clinton maintaining a lead over Republican Donald Trump. But with 57 days left, and a number of factors influencing the election, what comes next? NewsHour Weekend Special Correspondent Jeff Greenfield joins Alison Stewart to discuss where the race stands.

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ALISON STEWART, PBS NEWSHOUR WEEKEND ANCHOR:

With 57 days until Election Day, Democratic presidential candidate Hillary Clinton maintains a lead over Republican Donald Trump in most national opinion polls. An ABC News-"Washington Post" poll out this weekend shows Clinton favored by 46 percent of likely voters and Trump, 41 percent.

Statewide polls have also shown Clinton with a significant advantage in the Electoral College map that determines who wins the White House. But this election season has been unpredictable and there are more to these polls than just the status of the frontrunners.

To dig a bit deeper, we are joined by "NewsHour Weekend's" special correspondent, Jeff Greenfield.

Jeff, we can get caught up in the horserace of it all but there's something more to talk about in these polls.

JEFF GREENFIELD, NEWSHOUR WEEKEND SPECIAL CORRESPONDENT:

For me, one of the most interesting numbers is the relatively high percentage of voters who are either undecided at this point or leaning towards one of the third or fourth party candidates, Gary Johnson or Jill Stein.

This is — for this time in the cycle, that's unusually high. And I suspect this is because these are two historically unpopular party nominees. The other interesting thing is that, you'd understand why Jill Stein would be taking most votes away from Hillary Clinton, she's on the left, but you'd expect that a Libertarian like Gary Johnson would be drawing more from the right but if you match these numbers up, he seems to be marginally hurting her more.

And again, I can't prove this but my notion is, these are people who really don't want to vote for Trump but cannot or have not yet been persuaded to move to Hillary Clinton. And most significant part of Johnson's numbers is, in some states, he's in double digits. If he gets somehow, unlikely it's going to be, to 15 percent, he gets into the debates.

STEWART:

That's a game changer, right?

GREENFIELD:

A phrase I've never heard before. STEWART: Yes. It is indeed, because the one thing we know about third party candidates is both the presidential level with Ross Perot, back in '92 and it's statewide level is, you put an independent candidate in those debates and automatically he or she stands as an equal to major party candidates. That to me is one of the most significant things to watch before the presidential commission has to figure this out.

STEWART:

What do you think of the imbalance in the resources between the two campaigns? When you look at the numbers the Clinton campaign has, 6 to 1 in some cases in terms of what they're spending, why is that, would Trump ever try match that? GREENFIELD: He's now in the point last cycle, last couple of weeks, where he's only down two to one. I've talked to any number of people and said, well, how come that disparity hasn't shown up in the polls which in fact have tightened?

There are all kinds of explanations. One is that free media, what people see every night and on the news and get on their devices overwhelms paid media. Second is, well, maybe it did have an impact in increasing Trump's unfavorable ratings. Some people have complained that Clinton's messages isn't positive enough and then there are people who say, you know what, a lot of what spent in advertising may just be wasted.

We're not going to know the end of this campaign, what impact that had. But it's worth pointing out that in the primaries, Trump spent a tiny fraction of what his opponents spent on ads and get out the vote operations and won.

STEWART:

Let's talk about the economy, let's talk about the GDP, are those things going to end up being the most important thing ultimately?

GREENFIELD:

You know, there is a whole cottage industry in academia that say if you look — if you understand the right numbers, and they don't agree on the right numbers but they're basically economic, gross domestic product, is what happens in inflation or unemployment, some people throwing the incumbent president's approval ratings, but whatever the mix is, they will tell you that months in advance they have a pretty good idea who's going to win. And most of the time, if you go back and look, those pre-election year forecasts have looked good.

The problem is, this year, I've looked at five different forecast, two of whom said the Democrats will win, two of whom said the Republicans should have an edge, one says, I don't know. The point about that is, if the so-called fundamentals are marginals, come out like one or two point spread, then there's other stuff, ads get out the votes, the data analytics that we did a piece on some months ago, that Trump completely has not used.

That can make a difference and the stuff that academics often think doesn't matter that much, that we focus on the gaffes of what happens in a specific debate, even something like today's health episode that involved Hillary Clinton, they ordinarily say that has marginal impact. In the race where the fundamentals tell you this is going to be a close election, they may matter more than in the past.